Computing devices, such as notebook computers, personal digital assistants (PDAs), kiosks, and mobile handsets, have user interface devices, which are also known as human interface devices (HID). One user interface device that has become more common is a touch-sensor pad (also commonly referred to as a touchpad). A basic notebook computer touch-sensor pad emulates the function of a personal computer (PC) mouse. A touch-sensor pad is typically embedded into a PC notebook for built-in portability. A touch-sensor pad replicates mouse x/y movement by using two defined axes which contain a collection of sensor elements that detect the position of a conductive object, such as a finger. Mouse right/left button clicks can be replicated by two mechanical buttons, located in the vicinity of the touchpad, or by tapping commands on the touch-sensor pad itself. The touch-sensor pad provides a user interface device for performing such functions as positioning a pointer, or selecting an item on a display. These touch-sensor pads may include multi-dimensional sensor arrays for detecting movement in multiple axes. The sensor array may include a one-dimensional sensor array, detecting movement in one axis. The sensor array may also be two array, detecting movement in one axis. The sensor array may also be two dimensional, detecting movements in two axes.
One type of touchpad operates by way of capacitance sensing utilizing capacitive sensors. The capacitance detected by a capacitive sensor changes as a function of the proximity of a conductive object to the sensor. The conductive object can be, for example, a stylus or a user's finger. In a touch-sensor device, a change in capacitance detected by each sensor in the X and Y dimensions of the sensor array due to the proximity or movement of a conductive object can be measured by a variety of methods. The touch-sensor devices may include single sensor elements or elements arranged in multiple dimensions for detecting a presence of the conductive object on the touch-sensor device. Regardless of the method, usually an electrical signal representative of the capacitance detected by each capacitive sensor is processed by a processing device, which in turn produces electrical or optical signals representative of the position of the conductive object in relation to the touch-sensor pad in the X and Y dimensions. A touch-sensor strip, slider, or button operates on the same capacitance-sensing principle.
FIG. 1A illustrates a conventional touch-sensor pad. The touch-sensor pad 100 includes a sensing surface 101 on which a conductive object may be used to position a pointer in the x- and y-axes, using either relative or absolute positioning, or to select an item on a display. Touch-sensor pad 100 may also include two buttons, left and right buttons 102 and 103, respectively, shown here as an example. These buttons are typically mechanical buttons, and operate much like a left and right buttons on a mouse. These buttons permit a user to select items on a display or send other commands to the computing device.
FIG. 1B illustrates a conventional linear touch-sensor slider. The Linear touch-sensor slider 110 includes a surface area 111 on which a conductive object may be used to control a setting on a device, such as volume or brightness. Alternatively, the linear touch-sensor slider 110 may be used for scrolling functions. The construct of touch-sensor slider 110 may be the same as that of touch-sensor pad 100. Touch-sensor slider 110 may include a sensor array capable of detection in only one dimension (referred to herein as one-dimensional sensor array). The slider structure may include one or more sensor elements that may be conductive traces. By positioning or manipulating a conductive object in contact or in proximity to a particular portion of the slider structure, the capacitance between each conductive trace and ground varies and can be detected. The capacitance variation may be sent as a signal on the conductive trace to a processing device. It should also be noted that the sensing may be performed in a differential fashion, obviating the need for a ground reference. For example, by detecting the relative capacitance of each sensor element, the position and/or motion (if any) of the external conductive object can be determined. In one embodiment, it can be determined which sensor element has detected the presence of the conductive object, and it can also be determined the motion and/or the position of the conductive object over multiple sensor elements.
One difference between touch-sensor sliders and touch-sensor pads may be how the signals are processed after detecting the conductive objects. Another difference is that the touch-sensor slider is not necessarily used to convey absolute positional information of a conducting object (e.g., to emulate a mouse in controlling pointer positioning on a display), but rather relative positional information. However, the touch-sensor slider and sensor slider and touch-sensor pad may be configured to support either relative or absolute coordinates, and/or to support one or more touch-sensor button functions of the sensing device.
FIG. 1C illustrates a conventional sensing device having three touch-sensor buttons. Conventional sensing device 120 includes button 121, button 122, and button 123. These buttons may be capacitive touch-sensor buttons. These three buttons may be used for user input using a conductive object, such as a finger.
Capacitance sensing has been implemented in a wide variety of user interfaces of electronic devices to replace mechanical buttons in the electronic devices. Examples include touchpads on notebook computers, touchscreens, slider controls used for menu navigation in cellular phones, personal music players, and other hand held electronic devices. Capacitance sensing has many advantages over conventional cursor control devices, mechanical switches, and rotary encoders. A principal such advantage is the lack of moving parts, which allows capacitance sensing to provide great improvements in reliability, since there are no moving parts to wear out.
Some problems with conventional computing devices are that a mouse is a separate device and requires significant desk area to use; a track pad requires a large number of x-y sensors and significant computation to resolve directional inputs; and a joystick is physically bulky in three dimensions.